P31B-1389
The Effects of Solar Energetic Particle Events on the Lunar Plasma Environment
Solar energetic particle (SEP) events and the associated extremes in solar wind plasma conditions, magnetic fields, and energetic particle fluxes have significant effects on the local plasma environments at the Earth, other planets, and their moons. The Moon, which lacks a significant atmosphere or global magnetic field, lies fully exposed to the effects of these solar inputs. Previous investigations have demonstrated the direct coupling between solar drivers and the lunar plasma environment, revealing that increased energetic particle fluxes associated with SEP events act to charge the shadowed lunar surface to negative potentials as high as several kilovolts. In this presentation we explore the effects of large SEP events and other disturbances on the lunar plasma environment by comparing Lunar Prospector data during selected events with data from quiet times. We further consider the influence of SEP events on lunar surface charging, and investigate their effects on the structure of the lunar plasma wake. We also examine the impact of solar events on all aspects of the lunar magnetic field environment, including quasi-steady magnetic field structures associated with the wake and transient structures produced by local interactions with crustal magnetic fields.
P31B-1390
Lunar Surface Charging in the Magnetotail
The Moon spends most its orbit immersed in the solar wind plasma flow, where the resulting interaction has been relatively well studied. However, for about five days a month the Moon passes through the Earth's magnetotail, where it encounters the much hotter, more tenuous, and slower-moving plasma environments in the tail lobes (e.g., n = 0.02 cc, Te = 5.0e5 K, and V = -170 km/s) and plasma sheet (e.g., n = 0.2 cc, Te = 2.0e6 K, and V = -100 km/s). The lunar surface is electrically charged by the collection of charged particles from these various plasma environments, as well as by the photoemission of electrons from solar ultraviolet incident on the dayside. Photoemission often dominates on the dayside, where surface potentials are typically about 10 V positive. In contrast, on the nightside and near the terminator the electrons from the surrounding plasma tend to dominate surface charging - this results in a much greater variability in surface potentials, which can range anywhere from 10s to 1000s V negative. The most negative surface potentials on the nightside are usually found when the Moon traverses the hot plasma sheet region (typically about 500 V negative). The plasma sheet can be highly dynamic, especially during periods of enhanced geomagnetic activity. Therefore, encounters between the Moon and the plasma sheet can last anywhere from minutes to even days, and be extremely difficult to anticipate. Here we predict lunar surface charging during traversals of the magnetotail using spacecraft plasma observations as inputs to the model. We also investigate the dynamics of the magnetopause and plasma sheet boundaries at the orbit of the Moon using the OpenCGCM MHD global magnetosphere model.
P31B-1391
Review of ALSEP SIDE Results and Data Products
The ALSEP (Apollo Lunar Surface Experiments Package) SIDE (Suprathermal Ion Detector Experiment) instruments deployed on the Moon during the Apollo 12, 14, and 15 missions provided data for numerous investigations during the 1970s. These datasets are of great interest again as we prepare to return to the Moon. In a companion paper we present some initial results of combining Apollo SIDE data with more recent Lunar Prospector Electron Reflectometer data in order to develop an advanced lunar surface charging model. In this paper we review and summarize some of the SIDE results, together with features of the SIDE instruments and of the archived data products.
P31B-1392
Energetic Oxygen Flux at the Moon
As the Moon transits through the terrestrial magnetosphere it traverses three distinct plasma environments - the lobe, the plasmasheet and the low latitude boundary layer. While the plasma in the plasmasheet is primarily hydrogen, during storms, the concentration of oxygen ions can increase significantly. Even at concentrations of only a few percent, the oxygen ions can contribute the majority of the energy density. We will present results from 3D multifluid simulations quantifying the flux of energetic oxygen ions at the Moon during substorm and storm conditions. We will show how the concentration of oxygen, as well as the energy and flow direction of both hydrogen and oxygen, varies during active times. We will also discuss the role of the tail magnetic field in modulating the flux of higher energy ions at the Moon.
P31B-1393
AKR occultation observed by KAGUYA (SELENE)
KAGUYA (SELENE) is a Japanese lunar orbiter launched on September 14, 2007. The Lunar Radar Sounder (LRS) is one of the scientific instruments on board KAGUYA. It consists of three subsystems: the sounder observation (SDR), the natural plasma wave receiver (NPW), and the wave form capture (WFC). The WFC measures two components of electric wave signals detected by the two orthogonal 30 m tip-to-tip antennas from 100Hz to 1MHz. WFC-H [1] observes plasma wave spectra in 1-1000kHz and AKR (auroral kilometric radiation) is often observed. Occultation of AKR occurs when the satellite goes behind the moon. Its frequency dependence and effects of the relative positions of the earth, the moon with the satellite will be evaluated. How the occultation is useful for the source estimation of AKR will be examined. Effects of a single rounded obstacle on diffraction [2] will also be examined. Background AKR emissions will be evaluated by Geotail observation if possible. Acknowledgments: The SELENE project has been organized by the Japan Aerospace Exploration Agency (JAXA). The authors express their thanks to all members of the SELENE project team. References [1] Y. Kasahara, Y. Goto, K. Hashimoto, T. Imachi, A. Kumamoto, T. Ono, and H. Matsumoto, Plasma Wave Observation Using Waveform Capture in the Lunar Radar Sounder on board the SELENE Spacecraft, Earth, Planets and Space, 60, 341-351, 2008. [2] Recommendation ITU-R P.526-8, Propagation by diffraction, ITU, 2003.
P31B-1394
Plasma Wave Environment Measured by LRS/WFC Onboard KAGUYA (SELENE)
KAGUYA (SELENE) is a Japanese moon orbiter launched on September 14, 2007. The Lunar Radar Sounder (LRS) is one of the scientific instruments on board KAGUYA. It consists of three subsystems: the sounder observation (SDR), the natural plasma wave receiver (NPW), and the (WFC). The WFC measures two components of electric wave signals detected by the two orthogonal 30 m tip-to-tip antennas from 100Hz to 1MHz. By taking advantage of a moon orbiter, the WFC is expected to measure plasma waves related to solar wind-moon interaction, mini-magnetosphere caused by magnetic anomaly on the lunar surface and radio emissions to be observed from the moon. In the initial checkout phase of KAGUYA, from the end of October to middle of November 2007, data acquisition of the WFC was continuously performed almost 24 hours a day. In this period, KAGUYA is in the solar wind and several kinds of natural plasma waves were observed. In the higher frequency range around a few hundreds kHz, radio emissions such as AKR (auroral kilometric radiation) and type III bursts were observed. The most interesting spectral feature obtained by the WFC is intense electrostatic wave, which is assumed to be UHR or Langmuir wave. This wave is constantly observed in the frequency range of 10-20kHz in the sunlit region in the solar wind, while the frequency suddenly decreases in the shade (occultation) region. This feature is quite similar to the observation by the WIND spacecraft when WIND crossed the lunar wake at a distance of ~6.8 lunar radii. On the other hand, KAGUYA orbits the moon at an altitude of 100 km and the encounter of the lunar wake occurs in much closer region and varieties of frequency transition were observed at the boundary of the sun-lit and shade region depending on the orbital condition of KAGUYA, suggesting the spatial structure of the lunar wake Acknowledgments: The SELENE project has been organized by the Japan Aerospace Exploration Agency (JAXA). The authors express their thanks to all members of the SELENE project team.
P31B-1395
Sneaking of the Solar Wind Ions Into the Lunar Anti-subsolar Region Revealed by SELENE (Kaguya)
The moon spends more than 80 percent of its life staying in the solar wind (SW), where a quasi-vacuum region called the lunar wake is formed on the night side. The SW electrons with higher energy can come to the lunar night-side surface, while it has been thought that the SW ions are unlikely to approach the low altitude region on the night side because their thermal speed is much lower than the SW bulk speed. Here we show detection of SW ions sneaking into the anti-subsolar region at ~100 km altitude, using recent comprehensive measurement by a Japanese lunar orbiter SELENE (Kaguya). The sneaking of SW ions into the deepest lunar wake was accompanied by an enhancement of counter-streaming electrons along the SW magnetic field. A part of the ions detected in the anti-subsolar region came from the lunar surface, which means that the ions of solar wind origin reflected at the night-side surface. One possibility is that electron- rich wake environment strengthened the bipolar electric field at the wake boundary to let solar-wind ions approach the lunar night side, and the other scenario is that enhancement of ions in the wake let ambient electrons to come in. The sneaking mechanism of the solar wind ions in terms of plasma and electromagnetic environment around/inside the lunar wake will be discussed.
P31B-1396
Global Kinetic Simulations of the Interaction between the Solar Wind and the Moon
A density depletion region is formed on the Moon's nightside when the solar wind interacts and flows past the lunar surface, which acts as a diamagnetic obstacle removing plasma from the solar wind. To examine the formation of the Moon's wake-tail and the refilling of the density depletion region, a high resolution 3D global hybrid simulation is used. The hybrid simulation (particle ions, fluid electrons) uses realistic spatial scales for the lunar obstacle and the system size. The tail refilling process on the Moon's nightside can be described approximately by a plasma expansion into a vacuum driven by the thermal motion of particles along the interplanetary magnetic field lines. Electric fields created due to the pressure gradient at the edge of the density cavity further accelerates ions into the density depletion region and anisotropic distribution functions are formed. These anisotropic ion distribution functions lead to the generation of electromagnetic waves near the ion cyclotron frequency along the length of the wake-tail further downstream. A density increase at the center of the plasma depletion region also tends to form downstream where the ions beams from either side of the cavity meet and interact. Results will be compared with data from Wind when the satellite made flybys through the Moon's wake tail.
P31B-1397
Experimental program for investigating the basic physics of the lunar atmosphere
The tenuous lunar atmosphere is a surface-bound exosphere (SBE) similar to that found throughout the solar system, for example on Mercury, various icy satellites, over the rings of Saturn, on large asteroids, and on Kuiper Belt objects. Its time-dependent constituents arise from a dynamic balance between sources that may be sporadic (solar wind, sputtering, micrometeoroid impacts, outgassing) and loss mechanisms (escape, ionization). In an SBE, the atoms and molecules released from the surface follow approximately ballistic orbits, either returning to the surface or escaping to space without collisions. The mechanisms by which the lunar atmosphere is formed, in particular the role of constant micrometeoroid bombardment of the lunar surface, are subject to ongoing debate. We discuss here a series of open questions regarding the lunar atmosphere as well as an experimental program to address them. Particular outstanding questions include: What is the relative role of hypervelocity micrometeoroid impacts vs. Solar wind sputtering in regolith escape? Similarly, what is their relative role in the production of the observed Na in the exosphere? What is the physical mechanism by which He is released from the regolith, and under what conditions is it released with sub-escape velocities? How is implanted He freed preferentially to 40Ar? How do the particulate ejecta and plasma clouds released from micrometeoroid impacts interact, and how do they affect the lofting of fine regolith material? Laboratory investigation of these basic physical mechanisms can additionally provide input to the analysis and interpretation of the forthcoming LADEE measurements. The necessary experimental program considerations include appropriate sources, including a hypervelocity dust accelerator with the ability to accelerate micron-sized dust particles to realistic velocities (tens of km/s), and the capability for sputtering by solar wind constituent ions at realistic energies (~1 keV). Diagnostic considerations include the ability to measure the energy distribution, angular distribution, and composition of both vapor and particulate debris removed by both sputtering and micrometeoroid impact into realistic regolith material. In this talk, we describe the scientific and technical details of such an experimental program, including the specifics of how many outstanding questions can be directly addressed.
P31B-1398
Initial Global Mmapping of the Lunar Magnetic Anomaly by MAP-LMAG on SELENE (KAGUYA): Implication for the Lunar Crustal Magnetism
The magnetic field around the Moon has been successfully observed at a nominal altitude of 100 km by the lunar magnetometer (MAP-LMAG) on the SELENE (KAGUYA) spacecraft in a polar orbit since October 29, 2007. Here we report the initial global mapping of the lunar magnetic anomaly based on the observations during November 2007 to June 2008. Since the solar activity has been very low during the observation, an effect of the external field fluctuation is small enough to detect a weak signal of the lunar magnetic anomalies at ~100 km altitude. Distinctly identified are several anomalies: the Descartes anomaly, the Stöfler anomaly, the Crisium antipode anomaly and the Serenitatis antipode anomaly. However other magnetic anomalies observed at lower altitudes by the Lunar Prospector spacecraft are less clearly or hardly recognized in the present mapping result. Hence there is a significant difference in altitude dependence of the magnitude among the lunar magnetic anomalies, in particular, for the anomaly clusters at the northern edge of the South Pole-Aitken basin. This indicates that anomaly sources in the lunar crust have considerably different configurations such as depth and horizontal inhomogeneity of magnetization.
P31B-1399
Global mapping of the lunar crustal magnetic field using LP-MAG database and comparison with preliminary KAGUYA LMAG results
In the 2007 AGU fall meeting, we reported an objective scheme for estimating the spatial (3-d) distribution of the lunar crustal magnetic field from the satellite magnetometer data, and applied it to the Reiner Gamma magnetic anomaly on the nearside of the moon. Here, we provide the global vector map of the lunar crustal magnetic field using this scheme with Lunar Prospector Magnetometer (LP-MAG) low-altitude datasets. The scheme is a variant of the equivalent source method for estimating the magnetic field distribution. The features of our scheme are (1) utilising magnetic monopoles the equivalent sources, (2) simultaneous calculation for subtracting the trend due to the varying external magnetic field with the intensity of equivalent sources, and (3) Akaike's Bayesian Information Criterion (ABIC) minimization for determining the damping factor of the damped least square calculation, which endorses objectivity to the scheme. In this study, we select LP-MAG data of quiet times in all area of the Moon, and produce the global lunar crustal field map at altitudes of 40 km. Utilizing the data obtained at different altitudes, we were able to find more than two sets of reasonably stable data in all regions of the Moon, except for a few parts of the polar regions and the western mid-latitude region on the lunar farside. Following the visual inspection of the magnetic field distribution, the Moon is divided into 96 fan-shaped areas, where the scheme is individually applied. As a result of calculation, the magnetic filed is stably estimated. From the resultant equivalent poles representation, the magnetic field at the KAGUYA orbit is calculated and compared with the LMAG(Lunar MAGnetometer) observations. Their agreement is astonishing in several areas, showing that the scheme works well, as well as the good accuracy of the KAGUYA-LMAG observations.
P31B-1400
Analysis of tracking data and results from Kaguya (SELENE) satellites for lunar gravity field estimation
On September 14, 2007, the KAGUYA (SELENE) spacecraft were launched from Tanegashima Space Center in Japan. KAGUYA consists of three satellites: a main orbiter in a 100 km by 100 km circular, polar orbit, and two small subsatellites in 100 km by 2400 km (Rstar) and 100 km by 800 km (Vstar) elliptical, polar orbits. By employing 4-way Doppler tracking between the main orbiter and Rstar, the first direct tracking data of a satellite over the far side have been obtained, resulting in a newly determined global lunar gravity field. The existing 2-way tracking data set is furthermore complemented by precise differential VLBI tracking between Rstar and Vstar, providing a sensitivity perpendicular to the line-of-sight from station to satellite. This work focuses on various aspects of processing and analysing the tracking data from the Kaguya satellites for the main purpose of lunar gravity field estimation. This includes particulars of the data processing strategies, multi-satellite analysis and data weighting. Gravity models from Kaguya data are evaluated in terms of data fit and performance in orbit determination. The performance of the differential VLBI data in the orbit determination of the small subsatellites is also discussed, as well as their contribution to the gravity solutions. Results for the polar moment of inertia C/MR2 from the degree 2 coefficients, and for the lunar k2 Love number are also included.
P31B-1401
Preparations for Lunar Reconnaissance Orbiter gravity and altimetry missions
The launch of the Lunar Reconnaissance Orbiter is expected in early 2009. We present results of the preparations undertaken at the NASA Goddard Space Flight Center for the Lunar Orbiter Laser Altimeter (LOLA) instrument and the Radio Science experiment. A new lunar reference frame, vital to current exploration efforts for a return to the Moon, will be developed from the combined data sets collected by both experiments. In addition to collecting topographic data, LOLA will assist the Precision Orbit Determination of the LRO spacecraft. The 50-m total positioning requirement is very challenging due to the low altitude (50km on average) and the lack of radio tracking over most of the lunar far side. While commercial S-band tracking data will be the principal measurements used for orbit reconstruction, the unique five-beam altimeter enables the use of the altimetric cross-over technique with unprecedented accuracy. Previous simulations showed that the more numerous (by a factor of 25) crossings could greatly help in reducing the uncertainties in the recovered orbit. We show here that cross-track information contained in the acquired topographic swaths (compared to multiple two-dimensional profiles) can constrain orbits to a few meters horizontally and better than 50cm vertically. Swath cross-overs will be most valuable in mid-latitudes, where cross-overs are sparse and tracks intersect at shallow angles. A spacecraft physical model, for use in the GEODYN II orbit determination program, includes inter-plate self- shadowing in the calculation of the spacecraft cross-sectional area for solar radiation pressure. Simulations indicate that solar radiation effects on the orbit can be on the order of 10-20m. Because the thermal radiation forces are larger and more variable than on Mars, the current model of the thermal flux map was updated, with effects on the order of 1-5m. The benefit of using the self-shadowing model for the albedo and thermal forces is currently being assessed. Historical radio tracking data has also been reprocessed using the latest ephemerides (DE421) and improved force models (albedo and thermal radiation for all spacecraft; attitude model and estimated panel reflectivities for Lunar Prospector). The resulting normal equations will be important for the early LRO gravity solutions.
P31B-1402
Estimates of Sputter Yields of Solar-Wind Heavy Ions of Lunar Regolith Materials
At energies ~1 keV/amu, solar-wind protons and heavy ions interact with the lunar surface materials via a number of microscopic interactions that include sputtering. Solar-wind induced sputtering is a main mechanism by which the composition of the topmost layers of the lunar surface can change, dynamically and preferentially. This work concentrates on sputtering induced by solar-wind heavy ions. Sputtering associated with slow (speeds < the electron speed in its first Bohr orbit) and highly charged ions are known to include both kinetic and potential sputtering. Potential sputtering enjoys some unique characteristics that makes it of special interest to lunar science and exploration. Unlike the yield from kinetic sputtering where simulation and approximation schemes exist, the yield from potential sputtering is not as easy to estimate. This work will present a preliminary numerical scheme designed to estimate potential sputtering yields from reactions relevant to this aspect of solar-wind lunar-surface coupling
P31B-1403
Lunar Paleoregolith Deposits as Archives of Solar System History
The lunar surface is bathed in a variety of impacting particles originating from the solar wind, solar flares, and galactic cosmic rays. These particles can become embedded in the regolith and/or produce a range of other molecules as they pass through the target material. The Moon therefore contains a record of the intensity and variability of the solar and galactic particle fluxes. To obtain useful temporal snapshots of these processes, discrete regolith units must be shielded from continued bombardment that would smear the record over time. One mechanism for achieving this is the burial of a regolith deposit by a later lava flow. The archival value of such deposits sandwiched between lava layers is enhanced by the fact that both the under- and over-lying lava can be dated by radiometric techniques, thereby precisely defined the age of the regolith layer and the geologic record contained therein. The implanted volatile species would be vulnerable to outgassing by the heat of the flow at temperatures ranging between 300 and 1150°C. However, the insulating properties of the finely particulate regolith suggest that significant heating would be restricted to shallow depths. We have modeled the heat transfer between lunar mare lavas (of a range of temperatures, compositions, and thicknesses) and the regolith in order to establish the range of depths below which implanted volatiles would be preserved. We find that reaction-derived molecules (e.g., CH4, 20Ne, 36Ar) and weakly implanted particles (H2, He, H2O) would survive at depths of tens to <300 cm. Many other elements (e.g., C, N, S, CO, and N2) would survive outgassing at depths in the regolith of only a few cm (for a 1 m thick lava flow) to ~30 - 65 cm (for a 10 m flow). These results provide a basis for possible lunar exploration activities; obtaining useful archives of solar system processes would require extraction of regolith deposits buried at shallow depths beneath radiometrically-dated mare lava flows.
P31B-1404
Lunar Polar Subsurface Temperature History
We present thermal calculations for lunar polar subsurface locations to depths of 1 km in order to examine relative stability of water ice over lunar orbital history. The lunar orbit plane precesses in response to torques from the Earth and Sun. Cassini states are configurations in which the obliquity is adjusted so that the spin pole precesses about the orbit pole in the same period as the orbit pole precesses about the invariable pole. Such a state is the expected outcome of tidal dissipation within the Moon. Tidal dissipation within the Earth drives the lunar orbit outward, which in turn influences the rate of orbit plane precession. The Moon's original low obliquity Cassini state ceased to exist at a semimajor axis of about 34 Earth radii. Thereafter, the lunar spin pole reoriented into a new, higher obliquity Cassini state which slowly evolved into the Moon's current low obliquity [Ward, 1975; Siegler et al, 2007]. During the transition, there was a brief period of even higher obliquity values (~70 degrees). The duration of this transition is not well constrained, as it depends on the dissipation rate within the Moon at that time, but was likely of order 104-105 years. Though it is clear the lunar surface environment would be thermally unstable for ice during this transition, the same is not necessarily true for the polar subsurface. Furthermore, the period before this transition may have been thermally suitable for collecting volatiles in the near surface. It is therefore a worthwhile study to explore where early near surface ice might have relocated in response to orbital forcing. Here we relate a modeled subsurface thermal response to surface temperature forcing for a calculated lunar spin pole history. We examine the cases within and surrounding an idealized, currently shadowed, near polar crater that received direct illumination in earlier orbital epochs. We show depths at which temperatures would have provided a safe haven for ice if it were present and comment on its mobility. One of the motivations of this study is to understand the contrast in polar volatile inventories between the Moon and Mercury. Radar observations and thermal models support the conclusion that permanently shadowed polar craters of Mercury contain abundant near surface water ice. Thermal modeling shows that the Moon should also currently have near polar environments capable of preserving surface ice [Vasavada et al, 1999]. However, there is little conclusive evidence for surface lunar ice [Campbell et al, 2006]. A plausible explanation for this is that both bodies once had ice, but differing obliquity histories made lunar surface ice unstable and mobile, while mercurian ice remained unchanged. The present obliquity of Mercury is small, and has likely always been so. In contrast, the Moon experienced this period of very high obliquity, during which presently shadowed polar regions would have been fully illuminated.
P31B-1405
Changes of the lunar subsurface temperature inferred from seismic measurements
We use the seismic records obtained with the geophones of Apollo 17 seismic experiment at the Taurus Littrow landing site to measure variations of the seismic velocity in the lunar regolith. From the eight month long noise records we retrieve Green's functions between the sensors for successive 24 hour periods. By comparing the Greens functions of the different periods we observe cyclic variations of seismic velocity. Spectral analysis suggests that the variations are related to the influence of the sun rather than to the influence of the Earth. This implies that the temperature changes between lunar day and night speed up or slow down the seismic waves. With finite difference simulations we show that the observations are in accordance with expectations based on current knowledge of the thermal properties of the lunar regolith. A long term variation is also observed that is in phase with variation of solar energy flux due to distance changes between the Earth-moon system and the sun.
P31B-1406
Determining Engineering Properties of the Shallow Lunar Subsurface using Seismic Surface Wave Techniques
The geology of Earth's moon has previously been examined via telescopic observations, orbiting spacecraft readings, lunar sample analysis, and also from some geophysical data. Previous researchers have examined layering of the moon and models exist explaining the velocity variations in the mantle and core. However, no studies (or datasets) currently exist regarding the engineering properties of the shallow (<30 m) lunar subsurface. Engineering properties--like shear modulus and Poisson's ratio--are key parameters for civil engineering works, as they characterize the mechanical behavior of geotechnical materials under various types of loading. Therefore, understanding the physical and engineering properties within the upper 30 m of the lunar subsurface will be critical for lunar exploration if deployment of large structures, large-scale excavation, and/or landing of large spacecraft on the surface is desired. Advances in near-surface geophysical techniques, such as Multi-channel Analysis of Surface Wave (MASW), has greatly increased our ability to map subsurface variations in physical properties. The MASW method involves deployment of multiple seismometers to acquire 1-D or 2-D shear wave velocity profiles that can be directly related to various engineering properties. The advantage of this technique over drilling boreholes or any other geophysical technique is that it is less intensive, non-invasive, more cost- effective, and more robust because strong surface-wave records are almost guaranteed. In addition, data processing and analysis is fairly straightforward, and the MASW method allows for analysis of a large area of interest as compared to drilling boreholes. A new scheme using randomly distributed geophones (likely deployed from a mortar-type device) instead of a conventional linear array will be presented. A random array is necessary for lunar exploration because of the logistical constraints involved in deploying a linear or circular array robotically or by astronaut. Initial results indicate that robust dispersion curves (and thus subsurface models of engineering properties) can be obtained from the random array geometry. This random geometry will also be evaluated (a) for potential improvements in the resolution of the dispersion image and (b) as more accurate method for assessing azimuthal variations in the subsurface geology. Based on the extreme logistics imposed by lunar exploration and the anticipated engineering needs of lunar exploration, information obtained on the moon using this technique should prove to be a critical component of data acquisition.
P31B-1407
Cause of Deep Moonquakes
It is well known that the occurrence of deep moonquakes is highly correlated with the solid tides raised by Earth and the Sun. However, it has long been debated whether the tides are simply acting as a triggering mechanism for a release of accumulated tectonic stresses in the Moon's interior or the tides themselves are responsible for their generation, releasing tidally dissipated energy in the form of moonquakes. One way to test which of these two hypotheses is correct is to see when deep moonquakes occur relative to the long- term tidal amplitude variations caused by the changing position of the Sun relative to the eccentric orbit of the Moon around Earth. If the tides are simply acting as a trigger mechanism, deep moonquakes are more likely to occur when the tidal stress amplitudes are increasing, while if the tides are the main cause of deep moonquakes, they are more likely to occur shortly after the peaks in tidal stress amplitudes. We thus examined the frequency of deep moonquake occurrence as reported in the recently updated lunar event catalog relative to the difference between the anomalistic and synodic phases. Tidal stress amplitude reaches maxima when this phase difference is 0°, i.e., a new moon coincides with a perigee crossing, and when it is 180°, i.e., a full moon coincides with a perigee crossing. The result shows a general trend of maximum activity shortly following each of the tidal amplitude maxima, supporting the tidal generation hypothesis. However, an additional peak activity is found shortly before the tidal amplitude maximum at phase difference of 180°, also supporting the tidal triggering hypothesis in certain restricted cases. This secondary peak is limited only to some, but not all, deep moonquake nests. These trends are independent of whether the deep moonquake epicenters are located in either of the E-W hemispheres and in which of the tidal stress regimes as determined by the distance to the sub-earth point. Thus it appears that deep moonquakes generally represent release of tidally dissipated energy with additional triggered release of accumulated tectonic stress at a limited number of specific locations. However, this conclusion is provisional because the Apollo data did not cover the entire 18-year tidal cycle of the Moon.
P31B-1408
Lunar global feature of HF radar reflected from near-surface derived from Kaguya/LRS
To obtain information on the subsurface geological features of the Moon, the Lunar Radar Sounder (LRS) experiment has been carried out on-board the Kaguya spacecraft. From the data from an early period of the LRS observation from the middle of December 2007, we found clear evidence of subsurface strata extending below the nearside maria regions. We surveyed subsurface strata obvious below the nearside maria regions, and identified them in seven regions with a depth extending from 330 m to 1160 m [Ono et al., submitted]. The purpose of the LRS experiment on-board the Kaguya spacecraft was to better understand the subsurface sounding experiment of the moon to provide a global survey of the geological features of the lunar subsurface region by applying the HF radar method. Because knowledge of topographical features of the subsurface to a depth of several km is directly related to the history of lunar geology, it is necessary to accurately understand the origin and evolution of the moon. In this presentation, the global distributions of some characteristics features of the reflected echoes are shown. Global distribution of the echo power from lunar surface shows the clear dichotomy, whose values are distributed from -90 to -73 dBV. The mare regions on nearside represent the strong echo power. The echo power of the Mare Serenitatis, and Ocean Procellarum are distributed around -75 dBV. The highland regions represent the weak echo power. The echo power of the Aitken basin is distributed around -83 dBV. This echo power map has a good correspondence with a visible map of the lunar surface. Note that the surface echo power is related to several physical quantities such as the surface roughness, the reflectivity, the dielectric constant, and the porosity. To derive the global features of the physical quantities such as the reflectivity, the dielectric constant, the roughness, and the porosity, we need to attempt a numerical simulation to discuss roles of each physical quantity for each characteristic.
P31B-1409
Small Radar-Bright Crater Populations as a Guide to Mega-Regolith Thickness in the Southern Lunar Highlands
The southern highlands of the Moon comprise superposed ejecta layers, individually up to a kilometer in thickness, from the major basins. The radar properties of smaller (1-16 km diameter) impact craters that penetrate into this layered mega-regolith and excavate material from depth provide insight into the variability of mega-regolith depth above a postulated basement of large crustal blocks. We observe a significant difference in the population of radar-bright craters, 1-16 km and larger in diameter, between regions of the southeastern nearside highlands north and south of approximately 48°S latitude. There are about 1/3 fewer radar-bright craters south of this line than to the north, broadly coincident with the mapped boundary between southern deposits mapped as pre-Nectarian age and those of Nectarian to Imbrian age to the north. This difference in small radar-bright crater population is consistent with a mega-regolith thickness of about 1.5 km in the north and 2.5 km in the south, a difference that we attribute to South-Pole-Aitken basin ejecta.
P31B-1410
Formation of an ilmenite-rich outer core in the moon
The size and composition of the lunar core are still debated. The main constraint on these parameters is the moment of inertia. However, different models can be constructed which fit the measured moment of inertia of the moon equally well. It has been suggested that a dense ilmenite-rich layer, which originally crystallized near the top of the lunar magma ocean, may have sunk to the center of the moon to form either a complete lunar core or an outer core on top of a metallic inner core. The second model seems more likely since this model combines the requirements for a lunar magnetic field, caused by an early dynamo in the lunar interior (requiring a electrically conductive core) with the fact that ilmenite is too dense to remain at shallow depths after crystallization. Using a 2-D cylindrical numerical thermo-chemical convection model, we have investigated the formation and gravitational stability of an ilmenite-rich outer core. In mantle convection models for the earth a constant gravity acceleration can be assumed. However, in the moon, gravity acceleration decreases quickly with depth due to the much smaller core mass fraction for the moon, Xc≈0.01--0.04 versus Xc=0.315 for Earth. Our convection results illustrate the importance of a depth dependent gravity distribution, showing a clear influence on the stability of an ilmenite- rich outer core. We have investigated core stability by varying two parameters, density and the internal heating rate of the ilmenite-rich layer. Varying these parameters changes the compositional and thermal buoyancy of the dense layer. These two effects counteract and are therefore studied seperately. The parameters are varied within reasonable bounds from experimental data and theoretical calculations. The density and thickness of the ilmenite-rich layer are varied, assuming a constant mass of the ilmenite, mixed with a pyroxene with a Mg# between 20 and 40. The internal heating of the layer was varied using different assumptions for the behaviour of heat producing elements during lunar mantle overturn, while the total internal heating of the model was kept constant. From the modelling results we conclude that it is possible to form a stable outer core of ilmenite-rich material. This requires a relatively thick and dense ilmenite-rich layer. For a lower density or thinner layer, the ilmenite sinks to the top of the inner core, but it does not form a stable layer. The internal heating of the ilmenite-rich layer has only a small effect on the results, since the increasing temperature of the layer results in a reduction of the density contrast of less than 10% of the compositional density contrast. The thickness of the ilmenite-rich layer, required to form a stable outer core, is of the order of 60 km and a density contrast of 11--16% 5.2--5.4 wt. ilmenite) is required. If an original deep magma ocean is assumed (~1200 km), such a layer may indeed have crystallized at shallow depth beneath the lunar crust.
P31B-1411
UV Activation of Highly Mobile Electronic Charge Carriers in Gabbro and Gabbro Dust
UV irradiation activates highly mobile electronic charge carriers in igneous rocks including basalt, gabbro, and anorthosite. These charge carriers have the remarkable property that they can flow out of the irradiated surface layer and into the unirradiated part. They are defect electrons in the O2- sublattice, known as positive holes or pholes for short. Once activated, their lifetime is long. Traveling along the upper edge of the valence band, they cross grain boundaries. They can propagate over distances on the order of tens of centimeter or more. We have demonstrated that the phole charge carriers flow not only through solid gabbro but also through loosely compacted, finely divided gabbro dust. Being chemically equivalent to O- and, hence, to oxygen radicals, the pholes are highly reactive and highly oxidizing. If they are present in the lunar regolith, their chemical reactivity would have far-reaching consequences for human activity on the moon.
P31B-1412
Lofting of Triboelectrostatically Charged Particles From the Lunar Surface
Tribocharging of lunar regolith can occur by micrometeorite gardening and by anthropogenic interaction with the lunar surface. The tribocharged material may then be lofted into the exosphere by near-surface electrical fields created by solar wind and radiation effects. On the basis of a simple charge-to-mass ratio, the finest dust should be the most readily lofted. However, this model assumes that all particles in the affected material become charged, and that charging is a homogeneous process. Laboratory experiments have demonstrated that it is not simply the smallest particles that are subject to lofting. In an analog Debye-sheath electrical field between capacitor plates, tribocharged (vibrated) lunar simulant materials released both dust and silt/sand size materials into the electrical field. This observation was made with scanning electron microscopy of particle traps within the electrical field. The lab experiments also demonstrated an extreme inhomogeneity of tribocharging in the test samples. Ostensibly, the tribocharging vibrational energy was uniform throughout the sample, but observations of surface 'bursting', ' ballistic fountaining', and other phenomena indicated localized (millimeter-scale) electrical inhomogeneity. Theoretical modeling of tribocharging also suggests that there may be an optimum size fraction for charging. The coarsest particles undergo the greatest number of contact electrification events, but are too massive to be lifted. The finest particles are hidden or shielded from tribocharging by adhering to larger host grains in mechanical recesses. Medium-size particles receive moderate charging and are light enough to be lifted in the electrical fields; particles of several tens of microns may be optimally sized for lofting.
P31B-1413
Experimental Investigation of Dust Lift-off and Transport on Surfaces in Plasma
There is ample evidence from the Surveyor images and from in situ dust detection by the Lunar Ejecta and Meteorite (LEAM) experiment (deployed during the Apollo 17 mission) for significant dust lift-off and subsequent dust transport on the lunar surface. These near surface observations have been suggested to be directly connected to the dusty lunar exosphere that was indicated by Apollo astronaut sketches and the photometry of images taken from orbit. These observations remained largely controversial mainly due to the lack of our understanding of the physical processes responsible for dust mobilization. We have conducted a series of laboratory experiments to investigate the physics of dusty surfaces in a low-density plasma to investigate the possible mechanisms that can lead to dust lift-off and mobilization on the Moon. We report on dust transport experiments on a conducting plate. We found that when the plate is biased sufficiently negative, an initially small patch of grains spreads into a larger ring with a void at the center. Dust grains can spread over thick insulating plates, indicating that a 'hopping' mechanism is involved. The measured charge of individual grains, and the mapped potential distribution over the spreading patch are consistent with observed dust transport.
P31B-1414
LDEX: Lunar Dust EXperiment
The lunar dust environment is expected to be dominated by submicron sized dust particles released from the Moon due to: a) the continuous bombardment by interplanetary dust, and b) due to plasma-induced, intense, small-scale electric fields. To a good approximation, the impact-produced ejecta are expected to form a spherically symmetric, continuously present cloud, while the electrically lofted population is expected to be concentrated over the terminators, and remain highly temporally and spatially variable. The Lunar Dust EXperiment (LDEX) instrument is proposed for the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission for in-situ dust detection in orbit around the Moon. LDEX is based on the detection of ions generated in hypervelocity dust impacts. The instrument is capable of detecting submicron sized dust grains with impact speeds above about 1 km/s. Particles larger than about 0.2 microns can be detected individually, and the parameters of the impact signal yield the mass, velocity, and charge of the dust. Smaller dust grains, below the detection threshold for individual detection, are measured collectively as an average from a large number of impacts. With the extended detection size range, LDEX can verify the existence of the putative lunar dust-exosphere. LDEX has been recently developed at LASP, and it has a high degree of heritage based on similar instruments on the Ulysses and Galileo missions. An engineering prototype version of LDEX is scheduled for testing and calibration at the Heidelberg dust accelerator facility. The talk will briefly review the science goals and measurement requirements for in situ dust detection, as well as the capabilities of LDEX.
P31B-1415
The Electrostatic Lunar Dust Analyzer Instrument
Electrostatic levitation and transport of lunar dust remains an interesting and controversial science issue from the Apollo era. This issue is also of great engineering importance for designing human habitats and protecting optical and mechanical devices. The lunar surface is exposed to temporally and spatially varying solar wind plasma, UV radiation, and/or the plasma environment of the Earth's magnetosphere. Dust grains on the lunar surface collect an electrostatic charge and contribute to the large- scale surface charge density distribution. The Electrostatic Lunar Dust Analyzer (ELDA) instrument is under development to characterize individual mobilized dust particles. ELDA measures trajectory, charge and mass with high precision. The particles" trajectories are determined by the measurement of the electric signals that are induced when a charged grain flies through a position-sensitive detector system consisting of an array of wire electrodes connected to charge sensitive electronics. The mass of the dust is determined from the deflection in a region with strong electric field. A prototype of the trajectory detector has been constructed and tested. Here we present the instrument design, optimization of performance and the first experimental data.
P31B-1416
Rotary and Rotary-Percussive Drilling of Lunar Simulant
Honeybee Robotics has been developing a rotary and a rotary-preliminary drill system for planetary exploration. This is a test drill with a power rating of 1000 Watt, whose purpose it to test various drill bits and augers in rotary and rotary percussive operation. It is not optimized for power or mass but rather to acquire qualitative drilling data such as penetration rate, power, and torque, temperature, Weight on Bit, vibration energy and others. In addition, the design of the drill allows it to acquire drill bit temperatures and use pneumatic system (instead of augers) for removing of rock cuttings. The drill is designed to have a 1 meter stroke. In addition to the drill system, we have been developing a matching split vacuum chamber, which is 3ft wide, 3ft deep and 11 feet tall. The chamber consists of two smaller chambers (84 inches tall and 48 inches tall) assembled on top of each other. This allows for additional flexibility if only a smaller chamber is required for some testing. The chamber will be able to maintain pressure of below 1 torr. Maintaining sample temperature will be achieved by closed loop cooling system down to -40C or by using liquid nitrogen that allows a temperature of 77K. The test samples can be varied raging from solid rocks, to loose soils to icy soils and pure ice. The sample holder could also be integrated with temperatures for acquiring of thermal data during drilling process.
P31B-1417
Hydrocode Modelling of the South Pole-Aitken Basin-forming Impact
The South Pole Aitken Basin (SPA; probably the largest in the solar system) is about 2500 km in diameter and up to 13 km deep [1]. Simple scaling arguments suggest that this basin should have excavated the entire lunar crust [2]. However, remote-sensing observations indicate the floor of the SPA basin is predominantly lower crustal in origin [3-5], while gravity and topography data likewise suggest the presence of a ~40km thick lower crust [6]. This discrepancy might be due to either a low velocity impact [7] or, less likely, nonproportional scaling [6]. We use a high resolution, two dimensional hydrocode (Zeus [8]) to model vertical lunar impacts. Massless tracer particles were used to track and locate the crustal excavation cavity diameter and depth [8]. Cavity diameter scales as kinetic energy to the 0.3 power, in agreement with previous studies [9], and a kinetic energy of ~2.5e27 joules is required to form an SPA-size basin. The excavation depth: diameter ratio remained relatively constant at 0.14 +/- 0.03 over basins in the 500-2500 km diameter range [cf. 6]. For constant kinetic energies, lower velocities result in shallower excavation depths. However, even at the minimum velocity of 3 km per second, we found the excavation depth for SPA to be at least 100 km, greater than the likely crustal thickness. Shock melting products are found primarily at the surface of the transient crater. Based on our vertical impact results, we conclude that the entire crust was stripped from the SPA during the basin-forming impact and that the basin floor is primarily a solidified impact melt-sheet, perhaps with some lower crustal material mixed in [cf. 2,10]. [1] Spudis et al. Science 1994 [2] Lucey et al. JGR 1998 [3] Pieters et al. JGR 2001 [4] Jolliff et al. JGR 2000[5] Lucey GRL2004 [6] Wieczorek and Phillips Icarus 1999 [7] Schultz LPSC 28 [8] Nimmo et al. Nature 2008 [9] Housen et al. Icarus 1979. [10] Collins and Melosh LPSC 35
P31B-1418
Investigation of Lunar Impact Structures and Ridge Features by KAGUYA Altimetry (LALT) Data
The Laser ALTimeter (LALT) aboard a main orbiter of Japanese lunar explorer KAGUYA (SELENE) is a ranging instrument that measures the distance between the satellite and the lunar surface with accuracy of 5m by round trip time of the laser light every 1 second. Kaguya is in a polar orbit, the first global, precise, high-resolution topographic map has been obtained. Especially, previous experiments (ex. Clementine LIDAR) had not been gathered at high latitude regions (above 75-degree north and south). Our LALT measured that region for the first time. Using LALT data, we built a new lunar topographic mode and compared it with a previous model. As of LALT, the Unified Lunar Control Network 2005 (ULCN2005) was most precise lunar global topographic model based on a combination of Clementine images and a previous lunar control network derived from Earth-based & Apollo photographs, and Mariner 10, & Galileo images. Comparing our model with both ULCN2005 and Clementine LIDAR model, it is obviously shown that lunar topographic model would be totally (not only polar region, but also equatorial region) refined by our LALT model. LALT model can clarify the presence and shape of craters as well as large impact structure. Previously unresolved heights of central peaks of large craters are obtained. Several large impact structures in far side high land regions show multi-ring morphologies some of which were obscure in the previous map. LALT data clarified the presence of new ring structure around Moscoviense basin. The center of newly defined ring structure is offset from that of other Moscoviense rings. It means that, the new ring is not the third ring of Moscoviense, but it is predated impact structure. In near side, LALT data could express some tectonic ridges and rimas within the mare region.
P31B-1419
Status of Lunar Reconnaissance Orbiter Laser Ranging and Laser Altimeter Experiments
Lunar Reconnaissance Orbiter (LRO) will be tracked in one-way and two-way modes by microwave and optical systems in order to meet its global measurement requirements of 1-m vertical and 50-m horizontal position accuracy. Up to 28 Earth-station laser fires may be received at the antenna-mounted telescope. Earth returns and lunar returns from 5 beams will be time-tagged simultaneously with sub-ns precision by the Lunar Orbiter Laser Altimeter (LOLA) instrument. On-board timing is maintained by an ovenized crystal oscillator whose stability is better than 2E-12 over 1 hour. Absolute timing will be determined from radio tracking and orbital dynamics. A 12-cube retroreflector array mounted on the -Z panel is a facility for future laser tracking by an Earth station such as APOLLO, which is expected to provide absolute range and time calibration. In addition to the prime NASA NGSLR-Greenbelt facility and the MacDonald Laser Ranging System in Texas, the NASA MOBLAS-6 (South Africa) and MOBLAS-5 (Australia) stations may also participate. Proposals are anticipated from six international stations capable of tracking at 532.2 nm. Multiple stations separated by long baselines firing simultaneously will enhance this type of tracking. Together with LOLA altimetric crossover analysis such tracking will lead to even more precise orbit determination of LRO. Sensitivity to tracking coverage and geometry will be presented.
P31B-1420
Laboratory Visible to Far-Infrared Measurements in Support of the 2009 LRO Diviner Lunar Radiometer Compositional Investigation
We measured reflectance spectra of common lunar minerals spanning wavelengths from the visible to the far-infrared. These measurements provided critical data related to spectral variability of lunar minerals relevant to the Diviner lunar radiometer Compositional Investigation. Diviner will launch in early 2009 onboard the Lunar Reconnaissance Orbiter (LRO). Diviner is a nine-channel radiometer designed to study the thermal-physical and compositional properties of the lunar surface. Diviner has two solar channels (0.35- 2.8 μm; high / low sensitivity), three '8-micron' channels (7.55-8.05, 8.10-8.40, and 8.40-8.70 μm), and four thermal channels (13-23, 25-41, 50-100, 100-200 μm). The Diviner Compositional Investigation will use the 8-micron channels to determine the location of the Christiansen Feature, which is a good compositional indicator. The Christiansen Feature has a systematic behavior for silicates and shifts to longer wavelengths with increasing polymerization of the Si-04 tetrahedra. Therefore, the Christiansen Feature is located at shorter wavelengths for more felsic materials and longer wavelengths for more mafic materials. Additional compositional constraints will be gained using bulk solar albedo from solar channel data and spectral variation of thermal channels data. Even at Diviner's far- infrared spectral resolution, differences between mineral spectra are evident. It was important to have competent laboratory spectra measured across all Diviner-sensitive wavelengths. The spectra presented were measured on a Bruker IFS66/V Fourier transform infrared spectrometer at the University of Oxford Atmospheric, Oceanic, and Planetary Physics Laboratory. In order to cover Diviner's 0.3-200 micron response, we used three sources (quartz-tungsten, Glowbar, and mercury-arc) and several beam splitters. The measurements included the most common lunar minerals quartz, anorthite, enstatite, augite, forsterite, fayalite, and ilmenite and additional minor minerals. The samples were crushed and dry-sieved to different grain size seperates (< 30, 30-64, 64-120, and 120-450 μm). These minerals were also mixed into several analog lunar rock compositions. The location of the Christiansen Feature for 64-120 μm seperates in low vacuum was measured as follows: quartz, 7.38 μm; anorthite, 8.03 μm; enstatite, 8.38 μm; augite, 8.42 μm; forsterite, 8.88 μm; and fayalite, 9.38 μm. It was observed that the shape of Christiansen Feature changed and the location shifted slightly with changes in grain size and sample camber pressure. Some minerals also showed variations in solar albedo with grain size. Understanding spectral variations in common lunar minerals is critical to the success of the Diviner Compositional Investigation. These measurements represent an important first step. Future studies will expand the measurements to include a simulated lunar environment (i.e. emission measurements in vacuum with a cold back shield).
P31B-1421
Calibration of the Lunar Reconnaissance Orbiter Camera
The Lunar Reconnaissance Orbiter Camera (LROC) onboard the NASA Lunar Reconnaissance Orbiter
(LRO) spacecraft consists of three cameras: the Wide-Angle Camera (WAC) and two identical Narrow Angle
Cameras (NAC-L, NAC-R). The WAC is push-frame imager with 5 visible wavelength filters (415 to 680 nm) at
a spatial resolution of 100 m/pixel and 2 UV filters (315 and 360 nm) with a resolution of 400 m/pixel. In
addition to the multicolor imaging the WAC can operate in monochrome mode to provide a global large-
incidence angle basemap and a time-lapse movie of the illumination conditions at both poles. The WAC has a
highly linear response, a read noise of 72 e- and a full well capacity of 47,200 e-. The signal-to-noise ratio in
each band is 140 in the worst case. There are no out-of-band leaks and the spectral response of each filter
is well characterized. Each NAC is a monochrome pushbroom scanner, providing images with a resolution of
50 cm/pixel from a 50-km orbit. A single NAC image has a swath width of 2.5 km and a length of up to 26 km.
The NACs are mounted to acquire side-by-side imaging for a combined swath width of 5 km. The NAC is
designed to fully characterize future human and robotic landing sites in terms of topography and hazard
risks. The North and South poles will be mapped on a 1-meter-scale poleward of 85.5° latitude. Stereo
coverage can be provided by pointing the NACs off-nadir. The NACs are also highly linear. Read noise is 71
e- for NAC-L and 74 e- for NAC-R and the full well capacity is 248,500 e- for NAC-L and 262,500 e- for NAC-
R. The focal lengths are 699.6 mm for NAC-L and 701.6 mm for NAC-R; the system MTF is 28% for NAC-L
and 26% for NAC-R. The signal-to-noise ratio is at least 46 (terminator scene) and can be higher than 200
(high sun scene). Both NACs exhibit a straylight feature, which is caused by out-of-field sources and is of a
magnitude of 1-3%. However, as this feature is well understood it can be greatly reduced during ground
processing. All three cameras were calibrated in the laboratory under ambient conditions. Future thermal
vacuum tests will characterize critical behaviors across the full range of lunar operating temperatures. In-flight
tests will check for changes in response after launch and provide key data for meeting the requirements of
1% relative and 10% absolute radiometric calibration.
http://lroc.sese.asu.edu/
P31B-1422
Penetrators as planetary probes and MoonLITE a proposed UK-led lunar mission
While high velocity penetrator technology has been highly developed in terrestrial applications, their value to planetary science and exploration has yet to be demonstrated. Three missions have built and tested penetrators: Mars 96 – failed to leave earth orbit, Deep Space 2 – failed at Mars; and Lunar A – cancelled. Nevertheless, we will argue that the case for penetrators as planetary probes is strong. Penetrators provide a potentially low-cost and effective way to sample the sub-surface environment of planets, moons and asteroids at multiple sites within a single mission. Therefore, penetrators can create global networks and/or address local issues (such as the presence and nature of frozen volatiles in the permanently shaded craters of the Moon). The state of the art of penetrator technology will be described and its application to a variety of solar systems objects discussed. MoonLITE is a proposed UK-led 4 penetrator lunar mission for launch in 2014. The status of this mission will be described together with the outcomes of full-scale impact trials held in the UK during May 2008.